1. Field of the Invention
The present invention relates to an interleaver for demultiplexing light.
2. Related Background Art
An interleaver is a device configured to accept entry of signal light of multiple wavelengths (xcex1, xcex2, . . . , xcex2nxe2x88x921, xcex2n, . . . ) and demultiplex it into signal light in a first wavelength band xcex91 (xcex1, xcex3, . . . , xcex2nxe2x88x921, . . . ) and signal light in a second wavelength band xcex92 (xcex2, xcex4, . . . , xcex2n, . . . ), and is disposed in a repeater of an optical communication system or the like. Various types of such interleavers have been proposed heretofore and the known interleavers include, for example, those including a polarization separator, a wavelength filter, and a polarization combiner, and those including an optical system constituting a Mach-Zehnder interferometer. Another potential interleaver is one including an optical system constituting a Michelson interferometer.
Incidentally, the interleaver including the optical system constituting the Michelson interferometer employs a Gires-Tournois resonator including a semitransparent mirror with the transmittance of several ten % as one reflector, and total reflection mirrors, thereby achieving a flat-topped spectrum in which an insertion loss is flat near a maximum of the insertion loss in the vicinity of each signal light wavelength. In the case where the flat-topped spectrum is achieved by means of the Gires-Tournois resonator, it is, however, necessary to adjust the spacing between the semitransparent mirror and the total reflection mirrors in the nanometer order, and it is extremely difficult to attain a flat-top characteristic.
On the other hand, there are also cases where a transmission band near each signal light wavelength is set narrow to achieve a characteristic of excellent isolation between signal light wavelengths.
The present invention has been accomplished in order to solve the above problem and an object of the present invention is to provide an interleaver capable of achieving the various characteristics such as the flat-top characteristic, the excellent isolation characteristic, or the like by an extremely simple configuration.
An interleaver according to the present invention comprises an optical system having a first port, a second port, a third port, a half mirror, a first reflector, and a second reflector, and configured to split light having traveled from the first port to the half mirror, into two beams and direct the beams toward the first reflector and toward the second reflector, respectively, to split light having been reflected by the first reflector and having arrived at the half mirror, into two beams and direct the beams toward the second port and toward the third port, respectively, and to split light having been reflected by the second reflector and having arrived at the half mirror, into two beams and direct the beams toward the second port and toward the third port, respectively; and an etalon filter configured to cause a loss on either one of light incident thereto from the first port and the beams directed toward the second port and toward the third port.
In a preferred configuration, a free spectral range of the etalon filter to cause the loss on the light incident thereto from the first port is set at half of a free spectral range of the optical system.
In another preferred configuration, a free spectral range of the etalon filter to cause the loss on the beams directed toward the second port and toward the third port is set at the same as a free spectral range of the optical system.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.